The computer implemented method and system disclosed herein, in general, relates to answer supervision in a switched telephony network. More particularly, the computer implemented method and system disclosed herein relates to detection and remediation of false answer supervision (FAS) in a switched telephony network, specifically in a voice over internet protocol (VoIP) network.
False answer supervision (FAS) occurs when the telephony switch for the called party sends an answer signal although the called party has not answered. The FAS behavior by the switch bills the calling party incorrectly. For the VoIP industry, the widespread issue of FAS results in a loss of millions of dollars in revenue, dents profit margins, and damages relationship with customers.
Consider the occurrence of false answer supervision (FAS) in a VoIP call between peer gateways. The switch for a VoIP network is commonly known as VoIP gateway, or simply gateway in the context of VoIP network. The calling party uses an originating gateway to originate the call, and the called party receives the call via a terminal gateway. The originating gateway signals to the terminal gateway to setup a call. However, the terminal gateway responds with an answer signal before the call is answered, incorrectly billing the calling party because the originating gateway, on reception of the answer signal, assumes that the call has been answered and starts the billing meter for the duration of the call. Occasionally, the violation is more severe. For instance, the terminal gateway responds to the originating gateway with an answer signal, starts the billing, establishes the call to the called party via public switched telephony network (PSTN), finds that the called party is busy, and plays the busy tone, while the calling party is billed for an incomplete call.
False answer supervision (FAS) may be unintentional; for example, the downstream telephony service provider issues a false answer signal that the terminal gateway relays further to the originating gateway, or is malicious, for example, when the call is billed irrespective of whether the called party answers the call or not. If the call is answered by the called party and a successful conversation follows, the premature answer signal, i.e., answer issued prior to the called party going off-hook, may be tolerated. However, if the call is not answered due to the called party being busy or unavailable, billing such a call is a severe offense. The originating gateway's subscriber, the calling party, may detect this in the bill and demand cancellation of the charge. Billing prematurely answered calls may also result in loss of goodwill that can adversely impact the business for the originating gateway's service provider. It is in the interest of the originating gateway's service provider to vigorously pursue the matter of FAS with the service provider for the terminal gateway. The penalties imposed on the service provider for the terminal gateway may result in removal of the service provider from the routing table, leading to loss of voice traffic and revenues. When the consequences can be so severe and the adverse business impacts so grave, there is a need to detect FAS accurately.
Several attempts have been made by gateway vendors to detect false answer supervision (FAS), such as, detection of reverse polarity, timing since the last dialed digit, and detection and analysis of tones. The method of detecting reverse polarity applies to analog circuits and is not implemented in modern digital telephony circuits. The method is not suitable for cases where the gateways are configured to issue answer signal without the reception of reverse polarity. The method employing timing since the last digit is dialed, although to some extent successful, requires complex logic and remains plagued by false answer detection, or no detection when a call is in fact answered. These errors result in erroneous charges or no charges, and are a consequence of inexact answer supervision. Another method employs detection and analysis of tones using an apparatus that provides answer supervision to privately owned pay telephone equipment. The apparatus includes a microprocessor for analyzing tones received by the calling telephone while waiting for the called telephone to answer. This method provides complex tone analysis to distinguish between an answered call and noise caused by signals such as a busy signal. However, the implementation does not accurately detect false answer on all instances. Therefore, there is a need to achieve answer supervision without relying on circuitry that detects an answer by analyzing tones, waveforms, and noise on a transmission line to detect when a call is completed.
The current methods are only compatible with selected vendors and trunking interfaces of selected postal telephone and telegraph services (PTTs). Additionally, the methods discussed above are focused narrowly on false answer supervision (FAS), without regard to poor voice or audio quality calls, which similar to FAS, are another type of illegitimate calls. Hence, there is a need for a computer implemented method and system that detects FAS that is broadly compatible and does not falsely declare other types of illegitimate calls as FAS.